It is known to use hot isostatic pressure techniques to diffusion bond metal parts together. Diffusion bonding occurs when two mating surfaces are pressed together under temperature, time and pressure conditions that allow interchange of atoms across the interface. It is necessary that the surfaces to be joined are clean and that the variables of temperature, pressure and time are closely controlled, so that the necessary interchange of atoms may be achieved.
Hot isostatic pressing ("HIPping") is the application of high pressure gas (e.g. argon) at high temperature within a pressure vessel to the components to be joined. Gas pressure is applied isostatically so that there are minimal or no changes to the geometry of the components being joined. HIPping causes the collapse of internal porosity and the reduction of microporosity. Sintered powder and cast materials alike can be densified and consolidated, causing improved strength characteristics.
A HIP diffusion bonding process requires the efficient sealing of the components with a vacuum at their interface. This has hitherto been carried out outside the HIP vessel in a preliminary step with a vacuum pump and pipe. This is done by welding the edges of the components round the interface, welding a vacuum pumping pipe to the component, and evacuating the joint at temperature. The pipe is then sealed and the joint non-destructively tested to make sure the vacuum within the joint is intact. The joint between the components after this preliminary step is fragile, and great care has to be taken in moving the joined components to the apparatus where the HIP diffusion bonding process is to be carried out.
It is an object of the present invention to do away with the above-mentioned preliminary step and its attendant disadvantages.